Counting Scales

Decision support when purchasing counting scales:

The main task of the counting scales is the piece number determination with the help of the weight measurement.

So, it means that if there are 10 pieces on the scales and the total weight is 20 g, then the piece weight is 2 g. As a result, if the total weight is 200 g, there must be 100 pieces on the scales.

The determination of the number of pieces is based on the rule of three, whereby the counting scales always require the piece weight for the counting.

The transmission of the piece weight to the counting scales is the biggest difference between the individual counting scales and should be adapted to the task field.

In the simple models of counting scales, the counting function is a just one of many and not the main feature of these scales. The piece weight can only be determined by the scales with the help of the reference piece numbers. These counting scales look like regular scales and may not be recognized as counting scales at the first glance.

The process looks like this:

- The user places 10 pieces on the scales.
- In the counting function, the user is given the reference piece numbers of e.g. 5/10/20/50/100 etc., which the user has to confirm then. In this example, there are 10 parts.
- Since the scales know the total weight and the number of pieces, the piece weight can be determined by the balance itself.

This type of the counting scales requires, before each article change, the count of a reference piece number as well as the procedure described above.

It should be taken into consideration that not every part has exactly the same weight. Therefore, there may be total miscounts due to the weight tolerances of the individual parts.

In order to avoid these miscounts, the largest possible number of reference pieces should be used, especially for light parts, in order to obtain a representative average piece weight.

So, if several products are counted but they are frequently changed, the counting with these counting scales is impractical.

In this case, the counting scales with the piece counting function as their main task should be used. This type of scales differs significantly from regular scales.

This type of the counting scales offers the user three displays with different information. Thus, all the parameters – total weight, the piece weight and the number of pieces – are visible at a glance.

Another difference is the numeric keypad with the input keys for the numbers 0 ... 9, which provide fast and convenient value input as well as e.g. the following functions:

- Free adjustable reference piece number
- Direct input of the piece weight
- Summing function
- Direct input of the tare weight
- input of the target piece number / quantity

The process with this counting scales looks like this:

In the first step, the user must set the piece weight in the scales.

For this, the counting scales offer two options:

1. With the help of the reference quantity. The user places e.g. 18 pieces on the scales, press the reference piece number key and enters the number 18 using the input keys.

2. Direct input of the piece weight. If the piece weights have already been determined (see above "average piece weight"), this weight can be entered directly with the help of the number keys.

The count is then immediately visible on the three displays of the counting scales in the following order:

Total weights / unit weight / piece number (quantity)

 

If several batches of a product are counted, a total number of pieces can be determined by summing the individual counts.

Since the pieces to be counted are usually stored and transported in an overpackaging, the net weights must be determined for the counts. The net weight is therefore the pure weight of the pieces to be counted without the packaging.

The counting scales offer the possibility of entering the tare weight of the packaging using the number keys. In this case, unpackaging of the parts to be counted is not necessary anymore, if the tare weight is known.

Another interesting function regarding piece counting is the entering of the target quantity. After the registered number of pieces has been reached, an acoustic signal is given.

But even in case of these types of scales there are differences. The differences are determined and characterized by the extent of the individual functions. In the simpler counting scales, the input of data such as e.g. piece weight / tare weight / target piece number is carried out by the user. In the more complicated models of the counting scales it is possible to create databases which the user can access. This can be possibly done by scanning the item number. Another possibility is the communication of the counting scales with an inventory management system, where the required data can be retrieved and also the data can be stored after a finished counting.

Therefore, it is very important to clarify in advance how the working process with the counting scales should be arranged in order to carry out the time-consuming counting successfully and efficiently.

After the type of scales has been selected, a suitable measuring range must be specified. In general, a compromise has to be made between high resolution and high measuring range. Thus, scales with a higher, maximum weighing range have a lower resolution compared to the scales with a smaller weighing range.

Therefore, before purchasing a counting scale, the lightest piece to be counted must be determined. This piece weight should not be below the resolution of the counting scales, in order to allow a reliable measurement.

Example: If the lightest piece to be counted is 0.2 g, then the scales with min. 0.2g resolution should be used.

Based on this piece weight, the resolution of the scales can be determined, and there are different weighing ranges depending on the price range.

Finally, it should be considered what further steps after the count should be taken. Is it sufficient if the number of pieces only appears on the display of the counting scales or should the number of pieces with the indication of the article number be printed on adhesive labels or, if necessary, stored? These possibilities of data processing differ from one model of the counting scales to another and should be considered, before making the choice.

The verified scales are required for certain specified applications. Measuring instruments are subject to legal metrology if it is to be ensured that the displayed values of these instruments deviate only minimally from the actual value of the measurand. The devices that are to be verified must be constructed in such a way that they can measure reliably and that subsequent manipulation by the user is not possible or is immediately recognisable. The tolerance limits for the measurement results depend on the respective accuracy class. Depending on the weighing range and resolution, the verified counting scales can belong to accuracy class M I, M II or M III.

Thereby

Accuracy class M I	for fine scales,
Accuracy class M II	for precision scales,
Accuracy class M III	for commercial scales.

The calibrated counting scales of accuracy class M I usually have an automatic adjustment function with an internal test weight. This means that the scales automatically adjust to the new installation site when the location is changed. The gravity-dependent verified counting scales of accuracy class M II or M III, on the other hand, may only be used in the geographical area for which it has been verified.

Like other scales, the verified counting scales are loaded with special weights during verification, the mass of which is checked regularly. If the measured values do not deviate more from the actual mass than is permissible for the accuracy class, the scales receive a new verification seal and may further be used for the legal-for-trade applications until the verification period expires. If it is determined during the verification that the tolerance limits are exceeded for one or more test weights, the scales may no longer be used as the verified counting scales. If the scales are required for legal-for-trade applications, it must first be adjusted and then re-verified. The piece counting function is not checked separately during the verification. However, since the piece count is determined by dividing the determined weight by the recorded weight of the individual part, there is a direct correlation between the accuracy of the piece count and the accuracy of the weighing values.

The verified counting scale can easily be used for both legal-for-trade weighing and non-legal-for-trade piece counting. If they are used in the legal-for-trade sector, the scales must be registered with the local weights and measures / verification office. An application for reverification must also be submitted in good time before the verification period expires. This reverification is either carried out at the verification office or an application is made for the verification officer to check the verified counting scales on site at the user's premises.

A counting system is a device or installation for determining quantities. The counting system can be used to determine the number of parts, the number of people or vehicles or the quantity of bulk goods, liquids, gases or electricity. In many automated counting systems, the counting system adds up the individual quantities; in others, the number of parts is determined from a total quantity. The counting system can work mechanically or electronically and with or without interruption of the flow of goods, vehicles or people.

Different operating principles for quantity determination with the counting system
Since the elements to be counted are very different, various measuring or counting devices are used to facilitate quantity determination. For example, in continuous automatic traffic counts, the vehicles are often detected via induction loops embedded in the road surface. Pedestrians can be counted, among others, via radar, pressure, ultrasonic or infrared sensors or via video analysis. In the traffic counts, it is often not only the total numbers of vehicles or people over a certain period of time that are of interest, but also the distribution by times of day and days of the week and other additional information. The counting system that supports temporal evaluation is ideal for such evaluations. Not only for vehicle and people counts, but also in many other areas, manual counts with tablets, forms or mechanical counters are also carried out for single-case or key date-related records. While tablets and forms can also be used to record additional information, a simple mechanical counter only adds up the total number of the observed quantity.

The size of the count (people, vehicles, individual parts or packaging units) and the purpose of the measurement are decisive in determining which counting system is best suited. For quantity registration in the production process, it is also important how well the counting system can be integrated into the respective process. Optical, acoustic, volume and mass-based devices offer a range of possibilities. In order to achieve the set goals as effectively as possible, several counting methods can also be combined. Before investing in an elaborate counting system, it is essential to examine different options.

What should be counted?
First of all, it must be defined what is to be counted. It makes a big difference whether a large number of different parts or large quantities of the same or similar elements are to be counted. In the traffic counts on roads, the individual vehicles differ considerably in many characteristics, but they all also have common features that can be used for counts. The vehicles have contact with the road surface, a certain minimum height and they move in a certain direction, each with a fixed axle distance. As a rule, the vehicles to be counted also have sufficient distance between them. In production plants that produce similar parts in very large quantities, it is usually easier. The parts of a batch usually do not differ from each other and are often packed by type according to the piece count. For such parts as screws, nuts, dowels, washers and similar counting by piece weight is a good option. In the pharmaceutical industry, too, weight-based counting systems are often integrated directly into the packaging systems. If a new article is to be brought into such systems, it is usually only necessary to select the article number and the desired packaging unit from the data already stored in advance. The counting system then works with the stored article weight.

The more the elements to be counted differ in shape, size and weight and other characteristics, the more the possibilities of the automatic counting are limited. Movement possibilities and overlapping of the elements also make it difficult to correctly determine the number with some counting methods. In these cases, the movement is usually steered in a predefined direction and limited by the separating systems so that only one part after the other passes the position intended for counting.

Where should it be counted?
The place where the count is to take place also plays an important role. When counting outdoors, different disturbances are to be expected than in event, sales or production rooms. Even if counting is to take place in production, packaging or storage processes in the pharmaceutical, food production, chemical, plastics or metal processing industries, the requirements for the counting system and the environmental conditions differ considerably for the various products.

Profitability of the counting systems
Whether the purchase of a particular counting system is worthwhile also depends on how often it is used and what effects it has compared to the previous counting method. Not only the changes in the counting process itself have to be considered, but also possible additional benefits by speeding up the process flows, correct recording storage and transmission of inventory data and the reduction of the unmarked over- or under-quantities in the delivery of the products. It should be examined in detail for each possible variant which improvements can be achieved with the help of the new counting system.

Possible applications for a weight-based counting system
Whether during the inventory, goods receipt or picking and packing of the specified quantities, the quantities should be correctly determined. The weight-based counting system requires that the elements the number of pieces of which is to be determined differ only slightly in weight. Then the number of elements can be determined from the total weight of one or more partial quantities via the individual weight. Piece counting scales are often used for such applications. These scales, often equipped with a three-part display, numeric keypad and special counting functions, can be used individually or with additional larger weighing platforms as the counting system. The models with additional weighing platforms enable counting of very large quantities of similar parts. In fully automated processes, the piece counting scales are often integrated directly into the sorting or packaging machines.